► NH3, SO2, H2S and COS are emitted during different sludge conditioning processes. ► H2S and SO2 generation increase in the acidic environment created by H2SO4. ► Fenton peroxidation facilitates the formation of COS. ► CaO can reduce sulfur-containing gases emission via generation of calcium sulfate. ► CaO leads to the conversion of free ammonia or protonated amine to volatile NH3. Chemical conditioners are often used to enhance sewage sludge dewaterability through altering sludge properties and flocs structure, both affect odorous compounds emissions not only during sludge conditioning but also in subsequent sludge disposal. This study was to investigate emission characteristics of ammonia (NH3), sulfur dioxide (SO2), hydrogen sulfide (H2S) and carbonyl sulfide (COS) generated from sewage sludge conditioned by three representative conditioners, i.e., organic polymers, iron salts and skeleton builders, F-S (Fenton's reagent and skeleton builders) composite conditioner. The results demonstrate that polyacrylamide (PAM) has an insignificant effect on emission characteristics of nitrogen- and sulfur-containing odorous compounds, because the properties, sulfur and nitrogen speciations are similar in PAM-conditioned sludge and raw sludge (RS). Significant increases of SO2 and H2S emissions in the H2SO4 conditioning process were observed due to the accelerated decomposition of sulfur-containing amino acids in acidic environment. Fenton peroxidation facilitates the formation of COS. CaO can reduce sulfur-containing gases emission via generation of calcium sulfate. However, under strong alkaline conditions, free ammonia or protonated amine in sludge can be easily converted to volatile ammonia, resulting in a significant release of NH3.